Auchlossen Posted February 28, 2017 Share Posted February 28, 2017 I have a sedum covered flat roof of 153m2, with a slope toward one corner, and an upstand all round. There is a border of stone all round in the 'gutter' area. This is all standard design. The outlet is at one corner. What size should the outlet and downpipe be? There is some info about gutter sizing on gutter manufacturer websites, but I have not found any very convincing clarification of downpipe size. My calcs are: Roof area = 153m2 Rainfall factor x 0.0208 = 3.18 l/sec = 190.8l/min 100mm downpipe has flow capacity of 3.5 l/sec = 210 l/min 75mm downpipe has flow capacity of 1.97 l/sec is this correct? Can anyone advise sources please? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted February 28, 2017 Share Posted February 28, 2017 As always, your regs may be different, but here it's in Part H3 of the building regs: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf page 40. Link to comment Share on other sites More sharing options...
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